All "photographic" systems are limited in terms of the amount of the dynamic range of the original scene that can be reproduced. In a conventional photographic system the limiting element is typically the reflection print. This is true to an even larger degree if the final output is not a silver halide print but rather is a half-tone newsprint. In an electronic camera system the limiting element could be the image sensor (whether it is a solid state imager or a pick-up tube), the recording process, or the display media which could be soft, i.e. CRT display, or some sort of reflection print.
It is the photographer's goal to reproduce an image which is representative of how he "visualized" the original scene Most "snapshot" photographers are content with a "good" exposure, i.e. flesh tones are reproduced satisfactorily. But one of the attributes of the professional photographer is his ability to look beyond the problem of getting a correct average exposure and to the problem of reproducing the full tonal range of the image that he is visualizing within the constraints of the photographic system which he is using.
Ansel Adams developed what is called the Zone System in order to aid the photographer with a practical approach for representing a range of subject luminances, at the wish of the photographer, by a range of tone (or color) values in the final output. (See The Negative, by Ansel Adams, A New York Graphics Society Book, Little Brown and Company, Boston, 1981.) The Zone System requires the photographer to mentally divide the subject that he is visualizing into a finite number of zones which represent finite tone differences which he is trying to achieve in the final output. Next the photographer must measure the reflectance of subject luminance of a representative number of these zones and calculate his photographic exposure in order to "place" what he considers the important zones at the proper exposure level. If the subject luminance range is greater (high contrast) or lower (low contrast) than what he is visualizing, then he can do one of several things. A few examples are: if he is using artificial light, he can modify the lighting set-up; if he is using a negative film, he can modify the development time to change the contrast; if he is using an electronic camera, he could use digital signal processing to do likewise. In U.S. Pat. No. 4,304,473, entitled "Automated Exposure-Contrast Control Index Meter" by J. S. Shreve there is contained a comprehensive description of the zone system.
The present invention may be used to provide the photographer with a tool to quickly and easily measure the exposure of each of the aforementioned zones simultaneously.
The preferred embodiment of the present invention is incorporated in a digital, color electronic still camera system which includes a color display. In this embodiment, shortly after the subject is photographed, the captured image is displayed using pseudo-color techniques to represent the various "zones".
The present invention may be applied to a variety of types of photographic systems. Two examples are:
1. Hybrid film/electronic cameras of the type described in U.S. patent application Ser. No. 288,887, filed on Dec. 23, 1998 and entitled "Camera" by C. Bell, et al. PA1 2. Cameras of the type described in U.S. Pat. No. 4,837,628, entitled "Electronic Still Camera for Recording Still Picture On Memory Card With Mode Selecting Switch" by M Sasaki.
What these two systems have in common is their ability to electronically capture an image, process it, and display it on a display device. The present invention may be incorporated on any system that incorporates these functions.
An exposure meter which provides the photographer with an indication of the distribution of luminance values over a field of view is described in U.S. Pat. No. 4,671,655, entitled "Exposure Meter" by M. C. Heard. The present invention is a significant improvement over this invention in that it will provide the photographer with exposure information on a point-to-point basis within the image.